I can't remember what they call such seeds, but I think you don't want to run down to Mayo's and purchase just any old seed. Many of the seed producers now-a-days, produce hybrid seeds. You get one growing season out of them. The fruit doesn't produce seed for next year's crop. It may be called "Heirloom" or some such term.
I think it's smart to stock up on seeds. Usually they don't cost much and take up very little space. Just remember that you also need the proper tools for gardening. A tractor or a draft animal, both of which have to be "fed" as well. If you go mechanical, then you will need gas, oil and spare parts. If you go animal, then you have to store much more food and water.
A bugout bag is not going to be enough in a SHTF situation. Cities are not going to be the place to be if a situation goes on more than three days.